678 1 large molecules of this type by IETS. Our current effort focuses on studying chemical derivatives of these type of surfacebonded structures.
b
Acknowledgments. The authors wish to thank M. Ochoa and A. Poenisch for their technical support.
A
References and Notes ( 1 ) P. R. Moses, L. Wier and R. W. Murray, Anal. Chem., 47, 1882 (1975). (2) C. M. Elliott and R. W. Murray, Anal. Chem., 48, 1247 (1976). (3) Bruce E. Firth and L. L. Miller, J. Am. Chem. SOC.,98, 8272 (1976). (4) R. J. Burt, G. J. Leigh, and C. J. Pickett, J. Chem. SOC.,Chem. Commun., 940 (1976). (5) A. Diaz, J. Am. Chem. SOC.,99, 5838 (1977). (6) M. G. Simonsen, R. V. Coleman, and P. K. Hansma, d Chem. phys., 81,3789 (1974). (7) The Aldrich Libraw of Infrared Smctra. . . Charles J. Pouchert, Aldrich Chemical Co., Inc. (8) L. J. Bellamy, "The Infrared Spectra of Complex Molecules", Wiley, New York, N.Y., 1964. (9) IBM Postdoctoral Fellow, University of Karlsruhe, Germany. \
,
A. F. Diaz,* U. Hetzler? E. Kay IBM Research Laboratory, San Jose, California 95193 Received May 9, I977
Figure 1. Unretouched photograph of stereodisplay of atomic coordinates and connectivity of the ammonium perchlorate derivative of 12, taken on a Vector General Graphic System, programmed by S. M. Swanson and C. Morimoto. All unlabeled atoms are carbons. The perchlorate ion i s shown as i t appears with inversion disorder.
chlorate anion exchange (Dowex 1-X8, 38%). Generation of the protonated 1-pyrrolinium salt 11 was performed prior to irradiation by addition of 70% aqueous HC104.7
Photochemistry of N-Allyliminium Salts. A Novel Photocyclization Reaction Leading to Pyrroiidines
Sir: The photochemistry of unsaturated hydrocarbons containing nonconjugated ir chromophores linked through saturated carbon chains remains as one of the more interesting areas of organic chemistry. The number of unique molecular transformations observed have served as the basis for elucidation of the mechanistic details of excited-state reactions and for the synthetic utility of organic photochemistry. The di-ir-methane rearrangement,] which transforms compounds containing the 1,4-pentadiene grouping to vinylcyclopropanes, and intramolecular [2 21 cycloaddition reactions of 1,5-hexadienes and higher homologues* stand as exceptionally general examples of this point. Our interest in this area of photochemistry led recently to an exploration of the excited-state chemistry of compounds containing the N-allyliminium salt functionality (1) in which one of the two nonconjugated ir moieties is part of the imine (C=N) group. We wish to report the preliminary results of this investigation which demonstrate that these systems undergo a novel cyclization process to produce pyrrolidines, a reaction of potential synthetic and mechanistic interest.
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1
2
Initial investigations were conducted using the 5-phenyl2-isobutenyl-1-pyrroliniumsalts, 10 and 11, prepared by sequences starting with the known3 2,4,4-trimethyl- 1-pyrroline 1-oxide (3). Isobutenylmagnesium bromide4 was added to 3 (THF, reflux) to produce the hydroxylamine 4 (70%, mp 42-44 0C)5 which was converted to the nitrone 8 (HgO, CHC13, 98%). Addition of phenylmagnesium bromide to 8 (Et20, reflux) gave the 5-phenyl- 1-hydroxypyrrolidine 56a which was subsequently reduced (LiAlH4, AlC13, Et20,96%) to pyrrolidine 6 and chlorinated (NCS, Et20, 100%) furnishing the N-chloramine 7 as a mixture of diastereomers.6b Dehydrochlorination was performed using methanolic KOH and provided the 5-phenyl-2-isobutenyl- 1-pyrroline (9,72% after silica gel chromatography). The tetramethyl- 1-pyrrolinium perchlorate 10 (mp 126-127 "C) was derived from 9 by reaction with methyl iodide (EtOH, reflux) followed by per-
4, R , = H;R, = OH 5, R , = Ph; R, = OH 6,R, = Ph; R, = €4 7, R , = Ph; R, = c1
3
9
8
11
10
Irradiation of a solution of 11 (4.3 mM, from 9 and 2 equiv of HC104) in methanol using Corex-filtered lightsa led to consumption of the starting material and simultaneous production of a major photoproduct 12 which was isolated in pure form (44%)8b by neutralization (saturated NaHC03) and concentration of the photolysate followed by silica gel TLC (50% EtzO-hexane). Identification of 12 as 1,3,3,5,5-pentamethyl-2-exo-methoxy-4-phenyl-7-azabicyclo [ 2.2.1 ] heptane was made on the basis of spectroscopic data and by single-crystal x-ray diffractiong of its ammonium perchlorate derivative (mp 288-290 "C, from CHC13) (Figure l).'OPhotolysis of 11 (4.3 mM) in 25% aqueous acetonitrile was shown to follow a similar course; workup of the crude photolysate in the manner described above followed by preparative GLC (OV-101, 170 "C) gave the exo-azabicycloheptanol 13 (5896, mp 96-98 "C). Structural and stereochemical assignments to
&
&OCH3 12
13
14a,
R, = OCH,;R, = H
b, R, = H;R, = OCH,
Communications to the Editor
6782 13 were made on the basis of spectroscopic data and the conversion of this photoproduct to the exo-methyl ether 12 (NaH, CH,I, T H F , reflux). Irradiation of the N-methylpyrrolinium perchlorate 10 in methanol (2.8 mM) using Corex-filtered light afforded after base workup and silica gel T L C (EtzO) the 7-methyl-7-azabicycloheptyl methyl ether 14 (22%) as a 4:l mixture of exo (14a) and endo (14b) isomers. The conversion of 12 to 14a (dimethyl sulfate, K2C03, THF, reflux) serves to confirm the structure and stereochemistries of 14a and 14b. Importantly, dark control reactions conducted under a variety of conditions (e.g., refluxing aqueous or methanolic solutions of 10 and 11 for 24 h) failed to promote reaction of the isobutenyl- 1-pyrrolinium salts. Direct irradiation of the neutral pyrroline 9 in methanol, acetonitrile, or tert-butyl alcohol leads to consumption of the starting material, but does not produce the cyclization products observed above. In each case, trace quantities of a number of products along with polymeric materials are generated. Lastly, benzophenone-sensitized irradiation of 11 in methanol results in inefficient production of 12 under conditions in which 11 is completely consumed. Thus, the photocyclization reactions of 10 and 11 are definitely photochemical in nature and appear to initiate from the singlet excited states of the pyrrolinium salts. c10,-
15
I II
17
16
18
The generality of the photocyclization reaction has been briefly probed. The acyclic N-allyliminium perchlorate, 17, prepared by condensation of the tetramethylallylamine 15 with benzaldehyde followed by treatment of the derived imine 16 with perchloric acid, undergoes smooth photocyclization in methanol to produce (5 1%) the methoxypyrrolidines 18 as a 4: 1 isomeric mixture.' Although information on the mechanistic details of this novel photocyclization reaction is minimal, tentative yet reasonable rationale can be advanced. Intramolecular [2 21 photocycloaddition of the olefinic ir moiety to the singlet excited iminium chromophore would lead to the production of the short-lived aziridinium salt 19.12313 Collapse of this bicyclic intermediate by heterolytic cleavage of the internal C-N bond followed by rapid solvent capture of the resultant carbenium ion 20 would furnish the 3-substituted pyrrolidines. An alternate pathway having nucleophilic attack on 19 in concert with C-N bond cleavage appears unlikely since the preferrence for exo-methoxyl and -hydroxyl stereochemistry in products from reaction of 10 and 11 would not be consistent with displacement reactions of solvent a t C-7 of intermediate ammonium ions 21 having the 7-azatricyclo[2.1 .0.02,7]heptane~ k e l e t o n . ' ~
+
R +\r
19
20
I
teristics of iminium salt excited states. Studies to probe more deeply the mechanistic details and almost certain synthetic applications of this new excited state reaction are continuing. Acknowledgment. Support of this research by the donors of the Petroleum Research Fund, administered by the American Chemical Society, and by the Robert A. Welch Foundation is gratefully acknowledged. Financial support for the x-ray diffraction studies from N I H (GM-19455) is gratefully acknowledged. The authors thank Alice Friedman for her exceptionally competent technical assistance. Acknowledgment is made to Drs. E. Meyer and S. Swanson ( N S F PCM-22094) for the use of their graphic system and programs used to prepare unretouched pictures of the x-ray structures. References and Notes (1) S. S. Hixson, P. S. Mariano, and H. E. Zimmerman. Chem. Rev., 73, 531 (1 973). (2) W. L. Dilling. Chem. Rev., 66, 373 (1966). (3) R. Bonnett, R. F. C. Brown, V. M. Clark, I. 0. Sutherland, and A. Todd, J. Chem. Soc., 2094 (1959). (4) Super-magnesium used to prepare isobutenyl magnesium bromide was made by the method of R. D. Rieke and S. E. Bates, J. Am. Chem. SOC., 96, 1775 (1974). (5) Satisfactory spectroscopic and elemental analytical data were obtained for all new compounds. (6) (a) This material was obtained as a mixture of diastereomers from which one could be obtained in pure form by recrystallization from pentane (mp 115-1 16 OC, 39%). (b) The diastereomeric mixture (mp 51-54 OC) consisted mainly (9:l) of one isomer. (7) Addition of HCIOl to 9 cause a simultaneous decrease in the UV maximum at 234 nm and an appearance of a new absorption at 266 nm (log c 4.05) with an isosbestic point at 247 nm. Complete reversal of this change is noted upon addition of base. (8) (a) Irradiations were conducted in a preparative apparatus consisting of a Hanovia 450-W medium-pressure lamp in a water-cooled quartz immersion well, under an Ar atmosphere. Reactions were monitored by changes in UV and GLC characteristics of removed aliquots. Typical irradiation times to obtain nearly complete conversion ranged from 40 min to 33.75 h. (b) Spectroscopic analyses of the reaction mixtures before purification indicate that the yields for the cyclization reactions are nearly quantitative. The moderate yields obtained after purification must result from losses during chromatographic separations. (9) The compound crystallized in space grou F'2,/C with 4 molecules per unit cell, and cell constants a = 10.485 (4) b = 12.295 (4) A, c = 16.101 (6) A, /3 = 111.62 ( 3 ) O , V = 1926 (1) A3 at 3 OC. The space grou was confirmed on film. Data were collected in the 28 range 0 to 115 on a computercontrolled diffractometer equipped with graphite monochromater, using Cu KZ raidiation, with 8-28 scans. The 1974 out of 3092 data that had intensity greater than 3 u were used in a combination of direct methods and difference Fourier techniques to locate all nonhydrogen atoms. The R value is presently -0.14 with an apparent inversion-like dosorder in the perchlorate ion. Complete details of the crystallographic study will be published at a later date. IO) A trace (-1 % ) of the endo isomer of 12 in the photoreaction mixture is suggested by GLC analysis. 11) Assignment of stereochemistry to the major and minor isomeric photoproducts obtained from irradiation of 17 is not possible on the basis of the spectroscopic data accumulated to date. 12) (a) Although [2 21 cycloaddition reactions of olefins to the C=N bond are rare, recent reports by Swenton12band KochlZcindicate that the reaction efficiency increases when electron-withdrawing acyl groups are present on nitrogen. (b) J. S. Swenton and J. A. Hyatt, J. Am. Chem. SOC., 96, 4879. (c) R. M. Rodehorst and T. H. Koch, ibid., 97, 7298 (1975). 13) (a) Intramolecular [2 21 cycloaddition reactions of analogous 1,4dienes are known.'3b (b) E. Block and H. W. Orf, J. Am. Chem. Soc., 94, 8438 (1972); H. E. Zimmerman, P. Baeckstrom, T. Johnson, and D. W. Kurtz, ibid., 94, 5504 (1972). 14) (a) Although participation by nitrogen in stabilizing p-cationic centers is well known in acyclic and cyclic systems,14bthe ring strain present in the aziridinium ions 19 and 21 could be sufficient to minimize this effect. (b) R. 0. Hutchins and L. Rua, J. Org. Chem., 40, 2567 (1975). 15) Camille and Henry Dreyfus Foundation Teacher-Scholar Grantee, 1975- 1980. 16) Petroleum Research Fund Predoctoral Fellow.
21
An alternate pathway for this process, involving addition of the olefinic moiety to the excited iminium chromophore generating 20 directly, cannot be ruled out owing to our current minimal knowledge about the chemical and physical charac-
Journal of the American Chemical Society f 99:20 f September 28, I977
l,
8
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Patrick S. Mariano,*l5Jerome L. Stavinoha16 Rosemarie Swanson Department of Chemistry, Texas A & M Uniuersity College Station, Texas 77843 Received June 20, 1977
